1) Field of the Invention
This invention relates to an improvement in a trigger device for actuating a webbing tightener adapted to rotate a take-up spindle of a retractor in a webbing wind-in direction in the event of a collision of a vehicle or an air bag system for protecting an occupant from impact by an air bag promptly inflated with gas in the event of a collision.
2) Description of the Related Art
To protect an occupant in the event of an emergency such as a vehicular collision, passive restraint systems such as a webbing tightener and an air bag system have found wide-spread utility in recent years.
The webbing tightener comprises, for example, a pulley rotatably mounted on a take-up spindle of a retractor, a cable wound on the pulley, and a piston connected to a free end of the cable and slidably received within a cylinder. Pressure of expanded gas is caused to act on the piston so that a thrust is produced. This thrust then applies a tension to the cable, whereby the cable drives the take-up spindle of the retractor in a webbing winding direction, that is, in a webbing take-up direction. As a consequence, the webbing applied on an occupant is taken up in the event of an emergency. The webbing tightener is therefore provided with a gas generator for supplying gas pressure so that the gas pressure acts on the piston within the cylinder to apply a tension to the cable. This gas generator includes a detonating heater and an explosive. By a signal from a collision sensor, the detonating heater is energized and the resulting heat of the detonating heater detonates the explosive to generate gas.
The air bag system is accommodated, for example, in a steering wheel as a module, which is constructed of a center pad, a folded air bag, an inflator (gas generator), etc. In the event of a vehicular collision, the inflator is ignited to cause immediate combustion. The resulting combustion gas then instantaneously inflates the air bag, whereby the occupant's body is received by the inflated air bag and an impact on the body can be reduced. The air bag system is therefore equipped with a gas generator to supply inflating gas so that the air bag is inflated. According to the gas generator, an igniting charge is fired to ignite a propelling charge. As a result, the propelling charge immediately burns to generate inflating gas.
Gas generators for such webbing tighteners and air bag systems as described above therefore require a trigger device for firing an igniting charge subsequent to detection of a vehicular collision so that the gas generators can be actuated. As these trigger devices, those of the type that a firing heater arranged in an igniting charge is energized responsive to a signal from a collision sensor and the igniting charge is then fired by heat generated from the firing heater have been used commonly, for example, like the firing devices disclosed in Japanese Patent Applications Laid-Open Nos. HEI 2-24242 and 3-96456.
These gas generators however require vehicle body acceleration detection means, such as an acceleration sensor, for sensing a collision or the like of a vehicle to generate a firing signal and a control circuit for determining based on the firing signal whether or not the firing heater should be energized. This has led to the following problems:
1) More parts are needed, and the construction becomes more complex.
2) Wiring for individual electric components must be connected surely to assure the reliability of the system, so that the assembly work is not easy.
3) The system hence becomes expensive.
With a view to overcoming these problems, mechanical trigger devices have hence been developed like the trigger device disclosed in Japanese patent Application Laid-Open No. HEI 4-108049. According to such mechanical trigger devices, movement of a weight which also serves as an acceleration sensor for a vehicle body causes a firing pin to strike an igniter associated with an igniting charge, so that the igniting charge is fired by the resulting impact and such a complex control circuit is no longer needed.
According to the construction of the mechanical trigger device disclosed in Japanese patent Application Laid-Open No. HEI 4-108049, a trigger shaft is caused to rock by movement of a weight as an inertia body so that a stopper portion of the trigger shaft, said stopper portion having been in contact with a flange portion of a firing pin, is disengaged from the flange portion. This allows the firing pin to jut out under force of a compression spring and to strike a propelling charge.
The trigger device in which the firing pin is caused to strike the detonator arranged in association with the igniting charge as described above has however been pointed out to involve some problems. There is the potential problem that the stopper portion of the trigger shaft and the flange portion of the firing pin may rust or may stick together at areas of contact therebetween in the course of a long time. It is also difficult to keep the coefficient of friction stable at the areas of contact therebetween. Any attempt to increase the sensitivity leads to higher possibility of inadvertent actuation, thereby making it difficult to adjust the actuation sensitivity. This results in a system having low flexibility in design choice.